It is here shaken with 50 c.c. of a mixture of 25 vols. of ether with I vol.
of amyl alcohol, and the ethereal layer—which, in presence of cobalt, is
blue—separated, a few drops of concentrated thiocyanate solution being
used for washing. The extraction with the ether-amyl alcohol mixture
is repeated three or four times, until, indeed, it remains perfectly colourless
after the shaking. The various solutions containing the cobalt are then
shaken together in the same Rothe apparatus with dilute sulphuric acid,
into which the cobalt passes. The aqueous layer is separated—washing
with a little dilute sulphuric acid—and evaporated to dryness, the residue
being taken up in a little water, the solution made faintly ammoniacal and
any traces of nickel present with the cobalt precipitated with alcoholic
dimethylglyoxime solution. The precipitate is filtered off, the filtrate
evaporated in a small flask with nitric and sulphuric acids to destroy organic
matter, and the residual liquid placed in a tared crucible, where the excess
of the acids is expelled and the remaining cobalt sulphate then weighed :
CoS04 X 0-3804 = Co.
4. Determination of the Iron and Manganese.—The 400 c.c. of
solution left (8 grams of the sample)—quite free from hydrogen sulphide
—are diluted to about 1-5 litre, treated with hydrogen peroxide and made
alkaline with ammonia, heated and then left at rest for a short time on a
water-bath, the supernatant liquid being subsequently siphoned off and
the precipitated iron and manganese oxides collected on a filter. The
precipitate is dissolved in a little hydrochloric acid and the precipitation
with hydrogen peroxide and ammonia repeated, the precipitate being
filtered off after a short rest on the water-bath, washed with slightly ammo-
niacal water, dried, ignited and weighed.
This gives the ferric and manganese oxides together. The iron alone
is then determined either by titration or by separating it as basic acetate.
5. Determination of the Carbon.—3 grams of the sample are
dissolved on the water-bath in concentrated copper-potassium chloride
solution, the carbonaceous residue being collected on an asbestos filter,
washed, dried and burnt in a current of oxygen (see Determination of Carbon
in Iron, p. 168).
6. Determination of the Sulphur.—10 grams of the sample are
dissolved in nitric acids, evaporated several times with hydrochloric acid
and finally taken up in water and hydrochloric acid and filtered. In the
filtrate the sulphuric acid formed by oxidation of the sulphur is precipitated
with barium chloride solution. .
7. Determination of the Arsenic.—From 10 to 20 grams of the
sample are dissolved in nitric acid, the solution evaporated with sulphuric
acid until the nitric acid is completely expelled, the residue dissolved in
water, treated with 5-10 grams of ferrous sulphate and excess of.; hydro- ^
chloric acid and the arsenic determined by distillation (see Determination/;
of Arsenic in Iron). ^
5(5 • ^,1
Commercial nickel is more or less pure according to the processes used
obtain it. Of the impurities which it may contain (Cu, Co, Fe, Mn, Sn, Pb, S
Ca, AI, C, S, Si, SiO2, P, As), the most injurious, especially if the metal is 'er of these methods is washed with water, alcohol and ether, dried at